This invention relates to composite bodies and more particularly to a composite body having a base comprising a dry pressed powder.
Dry pressed and sintered bodies made of alumina, for example, are used in the semiconductor industry as substrates for integrated circuits and the like in which conductive pastes and films are formed in the fine lines that are 0.002" wide or less. After deposition of the conductive lines, the substrate is airfired at about 950.degree. C. causing the residue to adhere to the substrate surface. The substrate generally is made by compressing into a compacted body a spray-dried powder consisting, in this example, of alumina, flux, water and a binder, the powder being composed generally of spherically-shaped particles. Because of the shape of the particles, however, gap or voids exist between them and constitute minute defects in the substrate surface. The glassy phase produced by subsequent firing of the body often does not fill these voids which remain as surface defects. When the molecularly thin lines one to two mils wide are formed on the substrate, these surface defects can cause breaks or discontinuities in the lines and result in inoperative circuits.
Preparation of a substrate by casing, that is, doctor-blading a ceramic paste to form a tape, results in a body having a surface sufficiently defect-free to meet the requirements of microcircuit technology described above. An example of such a tape casting method is described in U.S. Pat. No. 3,786,854. While cast tape has a sufficiently smooth surface to accommodate fine line and high resolution circuitry, the formation of individual semiconductor substrates from such tape as by punching is much more difficult than with pressed powder resulting in punch pin breakage or deformation. In addition, the time required to dry green cast bodies at typical substrate thicknesses, say 70 mils, is uneconomically long.
Other techniques that may be employed in forming a substrate body having a substantially defect-free surface are building a laminated structure of layers cut from a thinner cast tape, and rolling a green mix to the desired substrate thickness. The disadvantages of the laminated body are the difficulty and time required in aligning and bonding the layers together. Rolled green substrates undergo dimensional shrinkage on drying and are difficult to form by punching as mentioned above.
The foregoing problem of producing substrates for the semiconductor industry is related to a problem encountered in the manufacture of high speed tools. Dry pressing and sintering of hard wear-resistant materials such as titanium nitride and titanium carbide to form cutting tools is not cost effective because of the relatively small cutting surface which uses these expensive materials. Current practice is to apply a thin layer of such materials to a less expensive tool body by the chemical vapor deposition technique. The disadvantage of this technique is that it requires use of dangerous chemicals and special gas scrubber apparatus for, toxic and corrosive exhaust gases.
This invention is directed to a composite body which overcomes the above disadvantages of semiconductor substrates and high speed tools.